1. Field of the Invention
The present invention relates to a load detecting device using an optical fiber.
2. Description of the Related Art
Vehicles such as automobiles and the like are equipped with catching detecting sensors for detecting that a foreign object is caught (trapped), for example, between the window frame and a side window glass which is driven by a power window device, or between the vehicle body and a motor-operated sliding door or back door. Pressure-sensitive sensors, which detect the pressing force which accompanies the catching of a foreign object (the reaction force received from the foreign object), are used as the catching sensors.
It has been thought to use an optical fiber sensor as the pressure-sensitive sensor (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-151615). The optical fiber sensor is structured so as to include an optical fiber which is elastic, a light incident means including a light source which emits light and makes a fixed amount of the light incident at the optical fiber, and a light-receiving body which receives the light which passes through the optical fiber. On the basis of the change in the amount of light which passes through, i.e., the change in the amount of light received by the light-receiving body, which change is caused by deformation of the optical fiber, the optical fiber sensor detects the external force (pressing force) which deforms this optical fiber.
Further, a push-button device using an optical fiber is known (see, for example, Japanese Utility Model Application Laid-Open (JP-U) No. 7-025527). In this push-button device, one of a pair of optical fibers, which are divided in two in the longitudinal direction and at which light usually passes from the one to the other, is deformed by the operation of a push-button, and the passage of light to the other optical fiber is blocked. A signal corresponding to the absence/presence of operation of the push-button (an on/off signal) is outputted. Namely, this push-button device is used as a switch.
A linear external pressure sensor using an optical fiber has been conceived of as a way of detecting an accident of a submarine cable (see, for example, JP-U No. 5-073604). A sensor core which structures this linear external pressure sensor is structured by projections or protrusions being formed at the outer peripheral surface of the outer layer covering of the optical fiber core wire. When external pressure is applied to a longitudinal direction position, localized lateral pressure is applied to the optical fiber at the interior by the projection or the protrusion at that position. In this way, the fact that external force has been applied to the linear external pressure sensor, and the longitudinal direction position at which this external force is applied, can be detected.
Further, a structure is known in which a pressure-sensitive sensor using a leaky optical fiber is built-in in the bumper of an automobile as a collision sensor (see, for example, JP-A No. 7-190732).
However, in the above-described conventional optical fiber sensors, in a case in which a load (pressing force) is received substantially uniformly over a wide range in the longitudinal direction, the load per unit area (unit length) is small, and therefore, there is the problem that the sensitivity is low. Improved sensitivity of detection has been desired in particular in applications in which the sensor is applied to a vehicle and detects the catching of a relatively large object such as the hand or arm of a person or the like.
Further, in the above-described conventional push-button device, one of the optical fibers must have a free end which can be displaced with respect to the other optical fiber, and a push-button which displaces this free end. In other words, the above-described conventional push-button device must be provided with the free end, the push-button and space for allowing the stroke thereof. Therefore, the device becomes large on the whole.
Moreover, in the above-described conventional linear external pressure sensor, projections or protrusions are formed at the outer peripheral surface of the covering. Thus, the number of parts or the amount of material which is used increase, and there is the problem that the cost increases. Further, this linear external pressure sensor is used in detecting accidents at submarine cables, and no consideration has been given to, for example, the handling performance, the assemblability and the like required for application to automobiles and the like.